Only run junit when there are junit_test targets in the graph.

Reviewed at https://rbcommons.com/s/twitter/r/2291/

src/python/pants/backend/jvm/tasks/junit_run.py

@@ -205,8 +205,9 @@ def _collect_test_targets(self, targets):
     java_tests_targets = list(self._test_target_candidates(targets))
     tests_from_targets = dict(list(self._calculate_tests_from_targets(java_tests_targets)))
 
-    if self._tests_to_run:
-      # Find matching targets to any requested test.
+    if java_tests_targets and self._tests_to_run:
+      # If there are some junit_test targets in the graph, find ones that match the requested
+      # test(s).
       tests_with_targets = {}
       for test in self._get_tests_to_run():
         # A test might contain #specific_method, which is not needed to find a target.
@@ -762,7 +763,7 @@ def execute(self):
       # that missing sources can be detected early.
       for target in targets:
         if isinstance(target, junit_tests) and not target.payload.sources.source_paths:
-          msg = 'JavaTests target {} must include a non-empty set of sources.'.format(target.address.spec)
+          msg = 'JavaTests target must include a non-empty set of sources.'
           raise TargetDefinitionException(target, msg)
 
       self._runner.execute(targets)

tests/python/pants_test/backend/jvm/tasks/BUILD

@@ -131,6 +131,7 @@ python_tests(
     'src/python/pants/backend/core/targets:common',
     'src/python/pants/backend/jvm/targets:java',
     'src/python/pants/backend/jvm/tasks:junit_run',
+    'src/python/pants/backend/python/tasks:python',
     'src/python/pants/base:build_file_aliases',
     'src/python/pants/base:exceptions',
     'src/python/pants/goal:products',

tests/python/pants_test/backend/jvm/tasks/test_junit_run.py

@@ -13,6 +13,7 @@
 from pants.backend.core.targets.resources import Resources
 from pants.backend.jvm.targets.java_tests import JavaTests
 from pants.backend.jvm.tasks.junit_run import JUnitRun
+from pants.backend.python.targets.python_tests import PythonTests
 from pants.base.build_file_aliases import BuildFileAliases
 from pants.base.exceptions import TargetDefinitionException, TaskError
 from pants.goal.products import MultipleRootedProducts
@@ -43,6 +44,7 @@ def alias_groups(self):
     return super(JUnitRunnerTest, self).alias_groups.merge(BuildFileAliases.create(
       targets={
         'java_tests': JavaTests,
+        'python_tests': PythonTests,
       },
     ))
 
@@ -137,6 +139,21 @@ def execute_junit_runner(self, content):
     # Finally execute the task.
     self.execute(context)
 
+  def test_junit_runner_raises_no_error_on_non_junit_target(self):
+    """Run pants against a `python_tests` target, but set an option for the `test.junit` task. This
+    should execute without error.
+    """
+    self.add_to_build_file('foo', dedent('''
+        python_tests(
+          name='hello',
+          sources=['some_file.py'],
+        )
+        '''
+    ))
+    self.set_options(test='#abc')
+    task = self.create_task(self.context(target_roots=[self.target('foo:hello')]))
+    task.execute()
+
   def test_empty_sources(self):
     self.add_to_build_file('foo', dedent('''
         java_tests(
@@ -147,7 +164,7 @@ def test_empty_sources(self):
     ))
     task = self.create_task(self.context(target_roots=[self.target('foo:empty')]))
     with self.assertRaisesRegexp(TargetDefinitionException,
-                                 r':empty must include a non-empty set of sources'):
+                                 r'must include a non-empty set of sources'):
       task.execute()